The present invention relates to a mixing device for mixing a liquid with a dry material, which comprises a mixing container for receiving the liquid provided with a screw thread, a threaded cap and a receiving insert for receiving the dry material between a top edge of the mixing container and the threaded cap prior to mixing.
There is a danger of dust formation during mixing of a liquid with the dry material, usually present as a powder or granulate. This leads to contamination of the environment and can cause harm or be troublesome to individuals performing the mixing process.
A typical example of this type of mixing process is the admixing of bleaching agent in the professional hair styling business. A bleaching granulate is taken from a flask in a measured quantity and fed to a stirring vessel. If the bleaching agent is present in the form of a bleaching powder, it is taken from a package by means of a measuring spoon and delivered to a stirring vessel. Prior to that or after that, a measured amount of a liquid is delivered to the stirring vessel with a measuring beaker. The liquid and the dry material are mixed with a brush to obtain a creamy mass.
The measuring of bleaching granulate or bleaching powder by a measuring spoon and/or a measuring cap is considerably inaccurate, so that frequently liquid or dry material must be added later to obtain the desired consistency. The open handling of the dry material in the form of a bleaching powder or bleaching granulate leads to undesirable dust generation.
To avoid open handling of the dry material with associated dust generation and to avoid the measurement inaccuracies--at least for the dry material, a receiving insert is used for receiving the dry material in a known mixing device of the foregoing type (European Patent Application EP 0 573 781 A1), which is inserted between the top edge of the mixing container and the threaded cap. In this known mixing device the receiving insert comprises an inserted container containing the dry material, whose wall facing the mixing container is torn off on screwing on the threaded cap, i.e. in the already closed state of the mixing container torn off by an upwardly protruding pin on the edge of the mixing container, so that the dry material pours out from the inserted container into the mixing container and can be intensively mixed with the liquid contained therein by agitation.
Dust generation is thereby prevented; however no individual measurement of the amount admixed in is possible, since the entire contents of the inserted container must be mixed. However very different amounts of bleaching agents are immediately required during mixing of the bleaching agent in different individual cases according to the amount of hair to be bleached.
A simple and reliable measurement of the dry material while avoiding dust generation in sufficiently few steps could consist in preparing the dry material in the form of tablets and feeding the required number of tablets to the mixing container before it is closed. A complete dissolution of the tablets in the liquid to obtain a homogeneous, user-friendly mass however is not guaranteed, because, on the one hand, the surface areas on the tables wet by the liquid are small in comparison to their mass, so that the dissolving process can proceed only slowly and because of that, among other things, in a closed mixing container--even if the container is made of a transparent material--there is insufficient control when the dissolving process is completely finished. In practice this possibility can be realized only when tablets are used as the dry material and mechanically comminuted in a mortar-like device to accelerate the subsequent dissolving process. This comminuting would however still be connected with an associated dust generation.